In general, construction machinery such as a wheel loader uses working fluid discharged from a hydraulic pump connected directly to an engine to operate a steering unit and a work tool. In particular, hydraulic systems that supply working fluid discharged from one hydraulic pump simultaneously to a steering unit and a work tool are currently in use. In such hydraulic systems, working fluid supplied to a steering unit and a work tool should be efficiently distributed, and an example of such distribution is shown in FIG. 1.
Referring to FIG. 1, working fluid discharged from a hydraulic pump 1 passes through a priority valve 2 and is supplied to a steering unit 3 and a main control valve 4. The working fluid supplied to the main control valve 4 is controlled in flow direction and supplied to an actuator of a work tool. The priority valve 2 is set to supply working fluid to the steering unit 3 first, and when a load sensing pressure (LS) of the steering unit 3 becomes low, the flow supplied to the main control valve 4 is increased and the flow of working fluid supplied to the steering unit 3 is reduced.
However, even when working fluid is first supplied to the steering unit 3 as described above, because an absolute flow of working fluid discharged from the hydraulic pump 1 is deficient when engine rpm is in a low range, the flow of working fluid supplied to the steering unit 3 is reduced. As a result, much effort is required to control the steering wheel, causing much difficulty in controlling the steering wheel.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.